# I Energy density of a 1D string?

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1. Mar 3, 2016

### James William

Hello,

As I understand there is a problem in physics where point-like massive (or charged, etc.) particles would have infinite mass/energy (or charge, etc.) density.

I'm curious how in the context of String Theory how we address the same problem?

I have come to understand Strings as 1-dimenstional objects from which I conclude they have no volume.

Do they have infinite energy density because they have no volume?

Thanks!

(This question comes from a discussion which can be found here for further context. https://www.facebook.com/notes/gm-j...stent-with-classical-physics/1006863599387308)

Last edited: Mar 3, 2016
2. Mar 3, 2016

### alw34

no

I skimmed the facebook discussion: generally, you can't go around 'willy nilly' plugging one equation into another and another without understanding the assumptions inherent in them. When you get infinities, say due to 1/r as r approaches zero, you might conclude oops there is an infinite result of some sort, and yet we never ever measure such infinities; hence a more rational conclusion is that the model [the equation] does not extend to zero r.

In the Standard Model of particle physics, quantum fields interact at points in a fixed background, flat space and time. So gravity which has so far been modelled in relativity as dynamic curvature in spacetime is not included. In string theory, the hypothetical is that those points of interaction are really one dimensional extended objects, strings. Elementary 'particles' are composed of tiny vibrating filaments of energy some hundred billion billion billion times smaller than an atomic nucleus, almost on the even tinir Planck scale. Different vibrational patterns produce different particles, which are in turn determined by different Calabi Yau shapes in space!. The key realization is that the detailed vibrational pattern executed by a string produces specific mass, electric charge, spin and so forth. The trick is to find these characteristics in the math, then figure out which characteristics match measurements.
Then there are theories with branes, two dimensional objects without volume. Same sorts of issues.
edit: where did that face come from? Does 'oops' create a face? cool! Almost like particles popping out of the vacuum.

3. Mar 8, 2016